This invention relates to conduction cooling of small, flat, heat generating devices such as integrated circuit (IC) chips, and more particularly, to an improved cooling device having a very low thermal resistance path between the heat generating devices and heat sink.
The introduction of large scale integration (LSI) and very large scale integration (VLSI) at the chip level and very large scale integration at the module level by packaging multiple chips on a single multilayer substrate has significantly increased both circuit and power densities. As a consequence, there arises the need to remove heat flux densities on the order of 1000kw/square meter at the chip level. To remove these high heat flux densities, there have been proposed various means of dissipating the heat. One limitation is that the cooling fluid (e.g., water) cannot come into direct contact with the chips or the area wherein the chips are mounted. Thus, a cooling hat must be incorporated between the chips and fluid which may be contained in a detachable or integral cold plate.
As VLSI chips increase in circuit density, switching speed and corresponding power, the thermal resistance of heat conduction systems, wherein an internal thermal device insert is placed between the chips and cooling hat, must be further reduced. In the thermal conduction module of Chu et al. U.S. Pat. No. 3,993,123, the internal thermal device insert is a piston which contacts the chip at one point. The thermal conduction module is very useful and successful in VLSI systems of the present but is not easily extendable to future high powered systems in all applications.
In the present state of the art there are many structures for achieving enhanced heat transfer Among these are intermeshed fin structures wherein the internal thermal device insert has substantially rigid fins which mate with corresponding fins in the cooling hat. One such fin structure is that disclosed in Horvath et al. U.S. patent application Ser. No. 198,962, filed May 26, 1988, the disclosure of which is incorporated by reference herein. These structures have the potential to provide improved thermal performance over single-surface structures, such as the piston in the thermal conduction module, because they comprise means for increasing the heat transfer area between the internal thermal device insert, which contacts the chip, and the cooling hat. Consequently, the thermal resistance between the chip and the cooling hat is lowered.
An inherent feature of these substantially rigid fin structures is that there will always be a gap, sometimes relatively large, between the intermeshed fins to accommodate chip tilt. This gap may be compensated by side-biasing or by filling the gap with a compliant, thermally conductive medium such as disclosed in Horvath et al. While such a fin structure does provide a low thermal resistance, the thermal resistance of the structure may be decreased by decreasing or, more preferably, substantially eliminating this gap.
An alternative structure has been proposed in Mansuria et al. U.S. Pat. No. 4,263,965 wherein a plurality of thermally conductive thin leaf shaped members are positioned within mating recesses of a cooling hat. Each of the thin leaf shaped members is independently spring-loaded against the chip. Chip tilt is accommodated at the chip-to-leaf interface. Thus, this design often times results in line-contact of the thin leaf shaped members against the chip, leading to a decrease in thermal efficiency of the module. Further, and perhaps most importantly, the leaf shaped members, while being thin, are nevertheless rigid as are the mating recesses of the cooling hat. Due to manufacturing tolerances, there will always be a considerable gap between the leaf shaped members and the cooling hat, thereby contributing to increased thermal resistance.
It has been proposed in certain structures to make the fins out of a flexible material
Thus, in Lipschutz U.S. Pat. No. 4,498,530, a plurality of flexible leaf elements are sandwiched between rigid spacer elements. The end result is a relatively rigid package, which is placed between the chip and the cold plate. Due to the fact that the flexible elements do not make good thermal contact with their corresponding flexible elements, the thermal resistance of this arrangement is unacceptably high. Also, since the entire structure is separate and distinct from the cold plate, an additional thermal resistance (i.e., arising from the interface between the cold plate and the structure) is included.
Tinder U.S. Pat. No. 4,707,726 discloses a heat sink having a channel therein and a plurality of semiconductor devices which are positioned within the channel. The semiconductor devices are side-biased against the side of the channel by a flexible member.
Berg U.S. Pat. No. 4,447,842 discloses a thermal device in contact with a chip. The thermal device has flexible fins which fit into channels of a cooling module. The cooling module is fitted with an expansible conduit which, upon expansion, causes the flexible fins to be forced against the sides of the cooling module, thereby aiding in the cooling of the chip.
Hanlon U.S. Pat. No. 4,190,098 discloses a cooling device for cooling a plurality of semiconductor devices. The cooling device comprises flexible fins which fit into the channels formed by the semiconductor devices.
Notwithstanding the previously described state of the art, there remains a need to increase the power dissipation capability of the cooling arrangement so as to be able to accommodate higher power chips.
It is thus a primary object of the present invention to have an improved cooling arrangement with increased power dissipation capability and decreased thermal resistance.
This and other objects of the invention will become more apparent after referring to the following description considered in conjunction with the accompanying drawings.